Method and system for transmit power control management in hspa

ABSTRACT

Determination of transmission power control commands in a UE by combining TPC commands received during DTX/DRX modes. The combining is done on those TPC commands which are received on different radio links after ignoring TPC commands which might be received in a DL slot overlapping with no UL transmission. The UE thus uses the combined TPC commands as derived at the time of entry into DTX for the second UL DPCCH preamble transmission which leads to increase in link reliability and subsequent conservation of power by the UE. The UE uses the same power as derived in the previous slot for resumption of transmission when all the TPC commands, received in the DL slot overlapping with no UL transmission, are UP. TPC commands for the transmission of the 2nd DPCCH preamble at transmission resumption is determined by combining stored TPC commands from each of the radio links that were received by the UE while entering into DTX gap and said TPC commands could not be applied with the newly received TPC commands.

TECHNICAL FIELD

The present invention, in general, relates to transmission power control management and in particular to transmission power control management in a UE of a HSPA network.

BACKGROUND ART

As per technical specification of 3GPP (3GPP TS 25.214 V07.04.00 and section 5.1.2.2.1) “When UL_DTX_mode=1, a TPC command is not required to be transmitted in any downlink slot starting during an uplink DPCCH slot which is in an uplink DPCCH transmission gap as defined in subclause 6C.2” meaning that a network is not required to transmit TPC commands to UE in F-DPCH slots which starts during a UL transmission gap. Also the specification says that “The UE shall ignore any TPC commands received in F-DPCH slot starting during an uplink DPCCH slot which is in an uplink DPCCH transmission gap as defined in subclause 6C.2” which means that a UE ignores TPC commands sent by the network that overlaps with the uplink transmission gap.

In case of an uplink DPCCH transmission gap as defined in the specification the UE adds together the values of TPC_cmd derived from each TPC command combining period in which a TPC command is known to be present and is not ignored as described above and which cannot be applied before the uplink DPCCH transmission gap, and applies the resulting sum of TPC_cmd values when the uplink DPCCH transmission resumes. Thus the TPC command applied at the time of resumption of transmission is a logical sum of the TPC commands derived from each TPC combining period.

Also as per the specification when UL_DTX_mode=1, a TPC command is not required to be transmitted in any downlink slot starting during an uplink DPCCH slot which is in an uplink DPCCH transmission gap as defined.

FIG. 1 illustrates an exemplary timing diagram in which a UL transmission resumes from a DTX/DRX gap and ends after a brief period of transmission. The TPC commands sent by the network and their subsequent interpretation by the UE as per existing description of 25.214 07.04.00 are shown. Thus as per 3GPP technical specification TS 25.214 V07.04.00 section 5.1.2.2.1 or 5.1.2.3 and release R1-071824, TPC commands received in F-DPCH at positions N_(OFF1)=0 and 2 for slot number #4 [as shown in FIG. 1] are not required to be transmitted by the network and should also be ignored by a UE if said UE received the same.

DISCLOSURE OF INVENTION Technical Problem

However as the output of γ equals 1 if the TPC commands from all the radio link sets are reliably “1”, or the output of γ equals to −1 if a TPC command from any of the radio link sets is reliably “0” the UE needs TPC commands of all the RLS to derive a TPC command value as UP.

Power control transmission decision thus determined by the UE using methods of the prior art during DTX/DRX modes is not efficiently handled. Further as in prior art UE uses 2 DPCCH preambles prior to transmission of the actual data, same power is used on both the DPCCH preambles at the time of resumption of transmission which leads to sub optimal use of the available preambles.

Technical Solution

It is accordingly the desideratum of the present invention to provide methods and system that eliminate, or at least significantly alleviate, the limitations and drawbacks of the prior art, including those described herein above.

It is accordingly a particular object of the invention to efficiently determine transmission power control commands in a UE by combining TPC commands received during DTX/DRX modes and thus obtain efficient power control convergence. Said combining is done on those TPC commands which are received on different radio links after ignoring TPC commands which might be received in a DL slot overlapping with no UL transmission. The UE thus uses the combined TPC commands as derived at the time of entry into DTX for the second UL DPCCH preamble transmission which leads to increase in link reliability and subsequent conservation of power by the UE. The UE uses the same power as derived in the previous slot for resumption of transmission when all the TPC commands, received in the DL slot overlapping with no UL transmission, are UP. However a DOWN command can be derived as per the existing 3GPP specification when the UE receives a single DOWN command on any of the radio links.

It is accordingly another object of the invention to determine the TPC commands for the transmission of the 2nd DPCCH preamble at transmission resumption by combining stored TPC commands from each of the radio links that were received by the UE while entering into DTX gap and said TPC commands could not be applied with the newly received TPC commands.

It is accordingly another object of the invention to determine the transmission power of the UE prior to resumption of the transmission, by using pattern of UL transmit power variations in the past and thereby setting the transmit power to be used on UL DPCCH at the time of the resumption. The UL transmit power could be deduced using extrapolation based on the UL transmit power history. The determined power requirement by the UE at the time of resumption of transmission also satisfies the SIR requirement at Node B to attain fast power convergence.

These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings.

Advantageous Effects

Thus the UE need not use same power level for the first 2 DPCCH power control preambles to be transmitted at DTX resumption. UE can adjust the power level to either ramp up or ramp down the power level from the 1st preamble to the 2nd preamble power to optimize on UE power consumption. Long term statistics can be used to make a decision on whether to ramp up or ramp down. It is beneficial to the UE in terms of power consumption even if blindly UE at DTX resumption uses 1 step size lower then the calculated UL DPCCH preamble power (Stored UL TPC commands which UE could not use at the time of entry into DTX) and then ramp up by 1 step size and transmits the 2nd DPCCH preamble.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the UL TPC commands combining,

FIG. 2 illustrates the system and method of deriving the TPC_Cmd at UL DPCCH Slot #1 for the purpose of the invention,

FIG. 3 depicts the method for the TPC command application for UL DPCCH slot #1,

FIG. 4 illustrates the method to determine the UL power at resumption with unequal DPCCH preamble power by using the power level of the last combined command and long term statistics.

GLOSSARY OF TERMS AND DEFINITIONS THEREOF

CPC: Continuous Packet Connectivity

UL: Uplink

DRX: Discontinuous Reception

DTX: Discontinuous Transmission

DPCCH: Dedicated Physical Control Channel

F-DPCH: Fractional Dedicated Physical Channel

UE: User equipment

TPC: Transmit power control

TPC_(gap): TPC commands received during a UL Transmission GAP

TPC_cmd_(N):Combined TPC command for the last combining period (Combining period N) before entry into DTX

TPC_cmd_(N-1): Combined TPC command for the previous to last combining period (Combining period N-1) before entry into DTX

TPC_Cmd_(Stored-Sum): Combined TPC command for the last 2 combining periods (Combining period N-1 and N) before entry into DTX. i.e. combining TPC_cmd_(N) and TPC_cmd_(N-1).

TPC_Cmd_(Latest): Combined TPC command derived from individual TPC commands received from RLs in response to UL DPCCH slot 0 transmission

RLS: Radio Link Set

RL: Radio Link

RoT: Rise over thermal

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention along with description necessary to bring out the invention will now be explained in detail.

Determination of transmission power control commands in the UE is achieved by combining TPC commands received during DTX/DRX modes. Said combining is done on those TPC commands which are received on different radio links after ignoring TPC commands which might be received in a DL slot overlapping with no UL transmission. The UE thus uses the combined TPC commands as derived at the time of entry into DTX for the second UL DPCCH preamble transmission which leads to increase in link reliability and subsequent conservation of power by the UE.

The said combining is performed such that the output of γ shall equal 1 if the TPC commands from all the radio link sets, that are not ignored according to 3GPP TS section 5.1.2.2.1, are reliably “1”, and the output of γ shall equal −1 if a TPC command from any of the radio link sets, that are not ignored according to 3GPP TS section 5.1.2.2.1, is reliably “0”.

The combining can also be performed such that the transmit power remains the same as 1st DPCCH preamble if the TPC commands from all the radio link sets are not received, or the output of γ equals to −1 if a TPC command from any of the radio link sets received by the UE is reliably “0”. That is, the output of γ shall equal 1 if the TPC commands from all the radio link sets, that are not ignored according to 3GPP TS section 5.1.2.2.1, are reliably “1”, and the output of γ shall equal −1 if a TPC command from any of the radio link sets, that are not ignored according to 3GPP TS section 5.1.2.2.1, is reliably “0”. If some TPC commands are ignored according to section 5.1.2.2.1 and TPC commands from remaining radio link sets are reliably “1”, use the same power as previous slot.

The method of combining the TPC commands received from a subset of RLS at TPC positions N_(OFF1)=0 and 2, in response to the 1st UL DPCCH preamble transmission is described. A soft decision is taken based on the TPC commands received in response to the 1st DPCCH preamble and the stored TPC commands received in the last 2 combining periods before UE entered into DTX.

FIG. 3 in conjunction with FIG. 2 explains the above method. The TPC commands received from each RL for the last 2 combining periods before entry into DTX are stored in the UE. If at the time of resumption, at TPC positions N_(OFF1)=0 and 2 UE receives any DOWN command then a power step DOWN command is applied to the next UL DPCCH command. However if at TPC positions N_(OFF1)=0 and 2 of F-DPCH slot #4, UE receives UP commands then the same TPC command positions in the stored combining periods received before entry into DTX is verified. If any of the stored TPC_cmd_(N) or TPC_cmd_(N-1) is DOWN and this was influenced by TPC commands at positions N_(OFF1)=0 and 2, then UE uses the combined TPC command TPC_cmd_(Latest) derived from F-DPCH slot #1 from TPC commands received at positions N_(OFF1)=0 and 2 [as shown in FIG. 2]. However if any of the stored TPC_cmd_(N) or TPC_cmd_(N-1) is DOWN and this was influenced by other RLS then UE uses the combined stored TPC_Cmd_(Stored-Sum). In this method UE need not use the same power on the second UL DPCCH slot as it used for first one, because it has valid TPC commands from network received at TPC position N_(OFF1)=0 and 2 which it can combine and apply.

The UE uses variable transmit powers on the 2 DPCCH preambles it transmits at the time of UL DTX resumption to suite the channel conditions prevalent at the time of resumption. FIG. 4 illustrates the method to determine the UL power at resumption with unequal DPCCH preamble. As shown in the figure UE can use 1 step lower power than the stored calculated power on the first preamble and then can ramp up to the stored calculated power for the second DPCCH preamble. This helps attain fast convergence and also conserve power for the UE. Various methods can be used to choose the powers of the 2 DPCCH power control preambles:

1) Using one step size below the calculated and stored TPC command on the 1^(st) DPCCH preamble and then ramping up to the calculated single TPC command for the for the 2^(nd) DPCCH preamble.

2) Using TPC statistics to find an estimate of the variation of the UL channel, the SIR target revisions in the DL from the previous DTX period to current DTX period, and follow the pattern to extrapolate the values of the 2 TPC commands.

3) Using long term TPC statistics and open loop uplink power calculation based on DL power to arrive at the transmission power for the first DPCCH preamble after DTX in case of long preambles after a long DRX/DTX period. Using either ramp up or ramp down based on the behavior of the long term TPC commands for the second DPCCH preamble after DTX. From the 3^(rd) DPCCH preamble onwards, TPC commands received from the base station are to be followed.

Thus the UE need not use same power level for the first 2 DPCCH power control preambles to be transmitted at DTX resumption. UE can adjust the power level to either ramp up or ramp down the power level from the 1st preamble to the 2nd preamble power to optimize on UE power consumption. Long term statistics can be used to make a decision on whether to ramp up or ramp down. It is beneficial to the UE in terms of power consumption even if blindly UE at DTX resumption uses 1 step size lower then the calculated UL DPCCH preamble power (Stored UL TPC commands which UE could not use at the time of entry into DTX) and then ramp up by 1 step size and transmits the 2nd DPCCH preamble.

It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description along with the drawings are not to be construed as limiting the invention and specific details as deemed necessary are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. 

1. A method for determining transmission power control command in a UE of a HSPA network by combining TPC commands, said TPC commands received during DTX/DRX modes wherein, said combining is done on those TPC commands which are received on different radio links after ignoring the TPC commands that might be received in a DL slot overlapping with no UL transmission, said UE using said combined TPC commands as derived for transmission of second UL DPCCH preamble and thereby leading to increase in link reliability and subsequent conservation of power by the UE.
 2. The method according to claim 1 wherein, same power level as derived in a previous slot using said combined TPC commands is used by said UE for resumption of transmission when all the TPC commands received in the DL slot overlapping with no UL transmission are UP.
 3. A method for determining transmission power control command during resumption of transmission of 2^(nd) DPCCH by a UE of a HSPA network in DTX/DRX mode by combining TPC commands wherein, said TPC commands from each of the radio links that were received by the UE while entering into DTX gap are stored by said UE.
 4. The method according to claim 3 wherein, said TPC commands could not be applied by said UE in previous TPC command determination.
 5. A method for determining transmission power control command prior to resumption of transmission of a UE of a HSPA network in DTX/DRS mode by using pattern of past UL transmit power variations and thereby setting the transmit power to be used on UL DPCCH at the time of the resumption.
 6. The method according to claim 5 wherein, said UL transmit power is derivable using extrapolation based on the UL transmit power history. 